Aircraft canopy transparencies are subjected to harsh environments, leaving them scratched, pitted, and crazed. This damage adversely affects the vision of the pilot and weakens the canopy structure. Replacement of a damaged canopy is extremely expensive, especially in cases where the damaged portion of the canopy is a large structure. A less costly alternative to replacement of the canopy is to rework the transparency by polishing to improve optical characteristics and to relieve stress in areas prone to cracking.
Prior methods for reworking aircraft transparencies have involved manual techniques which are labor intensive and are not always successful. In such methods, canopies are typically brought into a work area where a human expert inspects the transparency visually. Some canopies are obvious rejects to the inspector, but others require a very close inspection to identify flaws that exceed a critical depth into the plastic or to locate stress crazing. Canopies which fail inspection require the costly replacement of the transparencies. Canopies passing the inspection are manually sanded and polished to correct the flaws. Sanding in the vicinity of a flaw must be done expertly to avoid improper removal of transparency material that would introduce unacceptable optical distortion or remove excessive material and to avoid overheating of the plastic which weakens and discolors it.
Because manual restoration methods require subjective decisions regarding the severity of flaws and manual polishing to correct the flaws, the results are often inconsistent. Furthermore, manual restoration techniques are time consuming and expensive. The prior art has heretofore lacked an automated system for polishing aircraft transparencies to remove flaws. The method and apparatus of the present invention, as discussed in greater detail below, fulfills this need by providing a cost effective automated process for polishing such transparencies to obtain high quality, repeatable results.